Integrated circuit chips may be effectively cooled by using convective heat transfer to a suitable circulating liquid coolant. In the case of what is known as "C4 bonded flip chip packaging technology" which involves mounting and interconnecting typical circuit chips to a ceramic carrier by means of solder balls, a method is required whereby the liquid coolant is brought into intimate thermal contact with the silicon integrated circuit chip.
It has been recognized for some time now that liquid cooling promises to enable very compact arrangements for the cooling of arrays of very large scale integrated circuit chips, which are, of course, closely spaced to minimize propagation delays. Dense packing of these arrays rules out a system of forced air convection because of the large size of high performance forced air heat exchangers.
Accordingly, it has been proposed heretofore that, for example, heat be conducted through aluminum pistons spring-loaded onto the back of each chip, through cylinder walls surrounding the pistons, and into a heat exchanger circulating a liquid coolant. The thermal resistance of such a package allows a dissipation of about three or four watts per chip. However, even more compact confirgurations have been proposed by closely associating the heat exchanger with the silicon integrated circuit chip. Such a confirguration can be appreciated by referring to an article by W. Anacker entitled "Liquid Cooling of Integrated Circuit Chips", IBM Technical Bulletin, Vol. 20, pp. 3742-3743 of 1978.
Also, compact, high performance heat-sinking for very large scale integrated circuits has been proposed in (1) an article by Tuckerman and Pease entitled "High Performance Heat-Sinking for VLSI", IEEE Electron Device Letters, Vol. EDL-2, No. 5, 1981 and (2) an article by Tuckerman and Pease entitled "Ultrahigh Thermal Conductance Microstructure for Cooling Integrated Circuits", Proceedings, 1982 IEEE Electronic Components Conference. The first article discloses a compact heat-sink incorporated within an integrated circuit chip. This is done by forming microscopic channels for flow of the liquid coolant in the integrated circuit chip immediately adjacent the front side of the substrate where the circuitry is embedded; a cover plate overlies the back side of the chip or substrate for defining a manifold for communicating with the microscopic channels or grooves. Thus the system might be characterized as an integrated or directly cooled system. However, as pointed out in the second article cited above by Tuckerman and Pease, there are problems associated with such integration or direct cooling: it becomes necessary to construct sealed input and output manifolds ("headers") which connect the ends of the micro-grooves formed in the integrated circuit chip. One approach to the construction of these manifolds involves etching them directly in the silicon wafer; a PYREX cover plate containing an input and output port is hermetically bonded onto the wafer. The difficulty here is that such an approach is wasteful of silicon space. Moreover, it requires registration between the front side (i.e. the circuit side) and the back side (i.e. the groove side) of the wafer and cannot be used if the grooves are to be machined using precision sawing rather than anisotropic etching.
Another problem that presents itself is that if one desires to use anisotropic etching of the required deep grooves, a (110)-oriented silicon wafer is then required, but this is not an acceptable orientation for integrated circuit fabrication. Moreover, one might prefer to have the flexibility of being able to machine the grooves. However, this is also not possible in the case of the (100) orientation for a silicon wafer, which orientation is suitable for circuit fabrication. In other words, such mechanical methods of machining grooves in a (100) IC chip are impractical.
A further difficulty resides in the lack at the present state of the art for economically and reliably connecting the heat sink of the present invention to the liquid coolant source by means of a bellows device. In general, cooling bellows have been known, such as those described in U.S. Pat. No. 3,649,738. However, such devices have not provided for linking with the total area of the grooved heat transfer surface of a cooling chip.